In such plating apparatuses as mentioned above, it is necessary to monitor the plating solution to optimize such parameters as concentration of metal ions, pH level, and specific gravity and to suppress foreign particle density. Thus, conventionally a sample of plating solution is tested to check the metal ion concentration, pH level, specific gravity, and the particle density. Some of the components must be replenished while excessive foreign particles must be removed so that the metal ion concentration, pit level, specific gravity, and foreign particle numbers remain within permissible ranges.
However, such monitoring and pertinent operations for controlling the of the plating solution require periodic human work which is costly. Further, it is difficult with such operations to maintain the plating solution in an optimum condition. Still further, it is difficult to control the local temperature of the plating solution near the surface of a semiconductor substrate to be plated, since normally only the average temperature of the plating solution is monitored, often resulting in serious defects in the plated semiconductor substrate.